The electronics and computer industries are constantly expanding and pushing the limits of both performance and quality. The increased speeds and reduction in component size requirements have also required increased performance from cooling systems to prevent product degradation due to high performance temperatures. In general, heat transfer systems transfer heat from a heat-generating source to the surrounding air by the use of a combination of fans and heat transferring fins or heat sinks. As used herein, and in the appended claims the terms “heat transfer device” or “heat sink” will be understood to refer to all such devices that transfer heat from components using any combination of fans, fins or similar members.
Generally, heat transfer systems use a combination of conduction and convection or forced convection to transfer heat from heat generating components. A heat-producing component is placed in contact with the base of the heat transfer device. The heat transfer device is made of a material that readily conducts or transfers thermal energy through contact. Examples of such materials include aluminum and copper. The heat from the heat producing electronic device is transferred through the conductive base to the rest of the heat transfer device. The base of the heat transfer device is formed with a number of fins or other shaped extrusions that maximize surface area on the opposing side of the contact surface. The transferred thermal energy is then transferred from the conductive base to the fins. The thermal energy is then transferred from the large surface area of the fins to the surrounding medium (air or liquid) through convection. Convection is the flow of thermal energy from a solid to a liquid or gaseous medium. In most heat transfer devices, the use of stagnant air is not sufficient so the convection (or transfer of heat energy from the solid to the liquid/gaseous medium) is increased through forced convection. Forced convection includes the use of a fan or other transfer device to force the liquid/gaseous medium over the increased surface area of the fins. This increased flow of the liquid/gaseous medium increases the transfer of heat energy from the fins to the cooling medium thereby increasing the rate of cooling of the heat-producing component.
During the heat transfer process, the circulation of the air, and therefore the rate of transfer of the heat energy from the fins, is dependant upon the performance of the fan. If the fan is under performing or malfunctioning it may effectively reduce the efficiency of the heat transfer device and damage the electronic heat-producing component by allowing it to overheat. When the fan of a heat transfer device is malfunctioning, a great need arises to immediately replace it. Replacement of a faulty fan produces a number of problems due to the current manner of securing the fan to the base of the heat transfer device.
FIG. 6 illustrates a conventional heat transfer system. As shown in FIG. 6 and described in U.S. Pat. Nos. 6,345,664 and 6,351,044 (which are incorporated herein by reference), a cooling fan (50) is generally attached to the base (44) of a heat transfer device by adhesives (60). The fan (50) includes fan blades (52) that, when rotated, force air or other cooling medium over a set of fins (42). Power for the fan (50) is provided through a wire (56). The prior solution of using adhesive (60) to attach the fan (50) to the heat sink is not field-repairable and involves complicated heat sink removal procedures in the case of a failed heat sink fan. Additionally, the complexity of the removal procedures increases the amount of down time needed to replace a faulty fan and usually disturbs both the functioning of the heat producing component and the heat transfer device.
Other prior art solutions involve screwing the fan to the heat transfer device by placing screws through the fan housing. In many cases, however, there is no fan housing; rather the fan motor needs to be directly attached to the fin base of the heat transfer device. Screwing the fan to the base would be possible with a number of plastic fan designs, but the screw heads would be difficult to reach without disturbing the heat transfer device, and it is unlikely that fan vendors will be willing to incur increased costs by changing the design of their fan housings.
U.S. Pat. No. 6,109,340; U.S. Pat. No. 5,484,013; and U.S. Pat. No. 5,615,998 (incorporated herein by reference) demonstrate attempted solutions to the problems associated with connecting the fan by adhesives. In U.S. Pat. No. 6,109,340, the fan is integrally connected to the fan housing which is then designed to be easily removed and attached to the heat transfer device. However, by integrally connecting the fan to the housing it becomes impossible to replace the fan without replacing both the fan and the fan housing. This increases both replacement costs and manufacturing costs of the fan due to increased complexity of molds required to form the fan and housing as well as increasing the material required to manufacture the part.
Another possible solution to the removal problems associated with bonding the cooling fan with adhesives is addressed by U.S. Pat. No. 6,343,012 and U.S. Pat. No. 5,969,941. (incorporated herein by reference). In these patents, a retaining clip is affixed to the heat transfer device containing female threads. The fan is then manufactured with corresponding male threads integrally connected to the base of the cooling fan. To assemble the invention the male threads are affixed to the female threads of the retaining clip. While the fan is manufactured independently of the retaining clip, overall manufacturing costs of the fans are increased due to the increased complexity of the threaded base. Additionally, it is both difficult and time consuming to rotatably release a fan in compact situations such as cylindrically shaped heat transfer devices.